A seal in accordance with the preamble of the independent claim is known, for example, from published document US 2008/100000 A1. The seal is used, in particular, for sealing the gap between the rotor and the housing of a turbomachine.
It is an advantage of the above-described seal that the sealing gap is set by way of the volumetric flow which acts across the seal, and is therefore readjusted flexibly in the case of a different position of the rotor and the housing. This operating principle is implemented in what is known as the shoe which is suspended in a sprung manner on a carrier. This system is the main sealing system (also called the main seal).
Said radially flexible seal requires an axial auxiliary sealing system or an auxiliary seal which likewise seals the changing axial gap in a flexible manner. This takes place, for example, via two sheets which are equipped in each case with a spring system, are accordingly pressed on a carrier, and therefore close the opening gap in the direction of the shoe. In order that the two spring systems, that of the shoe and that of the auxiliary seal, can run in parallel in a low-friction manner and at the same time the region of the spring system for the auxiliary seals also remains covered, two components are provided, an intermediate plate and a cover. The latter have a play with respect to the main sealing system and a clearance among one another for the auxiliary sealing system. For the application in a gas turbine, said operating principle has to be realized by way of very intricate components. As a consequence, very high manufacturing accuracies have to be maintained, and a distortion of the components, both as a result of manufacturing inaccuracies and as a result of the influence of temperature, can jam the auxiliary sealing system, and the corresponding thin sheets of the auxiliary seal then cannot close the opening axial gap in the direction of the shoe completely as desired.